One thing I'm really hoping for(yet doubting will be in the game) is to be able change the aesthetics of spell when creating it.This way the starting fireball look won't be the only one.
That's not going to happen in the game, because spell making is not in Skyrim.
In any case, I'd definitely like to see more variety in clothing suited for "pure" mages, aside from the lack of unarmored, the boringness of the default clothes is another reason why in Oblivion, when I made magic using characters they still tended to combine magic with other skills, at the very least, I'd like for not all robes to look like retextures of the same design. I'd also like to be able to wear clothes under robes, I see no legitimate balance reason not to have that in a game with multiple armor and clothing slots, if anything, not having that is bad for balance as it means using robes is a bad idea, and that it's actually better to wear normal clothes.